Plant with rotating furnace for the melting without salt of aluminum with screening and recovery of the slags

ABSTRACT

A plant for the melting of primary and secondary aluminium, provided with a rotating furnace, internally equipped with a spiral element ( 11 ), that realizes the melting of the aluminium not using a salty bath, in association with a channel of pouring ( 13 ) set among the hole ( 4 ) of the rotating furnace and the spherical store basin ( 16 ) positioned on a lower plan, in a pit, and equipped with a rotating joint ( 17 ) that realizes a continuity of inclination with the channel of pouring ( 13 ) so that what is obtained is the direct and continuous flow of the fused metal in the store tank without interruption of the process of melting. The plant is also equipped with an automatic and continuous system of selection and recovery of the slag of fusion integrated in the same plant and a double system of canalization of the gases that allows a good cleaning of the pollutant agents and a remarkable energetic conservation in the furnace of melting.

TECHNICAL FIELD

Object of the present invention is a modular plant for the melting ofmetallic materials, especially aluminium scraps, comprising a rotatingfurnace characterized by the lack of use of a salty bath, and withdirect poured of the melted metal in a spherical store tank, anequipment for the selection and recovery of the slag of fusion and asystem of scavenging.

STATE OF THE ART

As it is known, the melting of the aluminium scraps, for the productionof ingots for alloys, and also the remelting of the same aluminiumingots is realized in the rotating furnaces, also called salty bathfurnaces, in which the sea salt (usually mixed with carbonate of soda,salnitro and yellow prussiato of potassium) is melted by the heatproduced in the furnace.

Salt is a good receiver and transmitter of heat and its addition isuseful as cover agent to prevent the oxidation of the metal in fusion.At almost 1000° C. it reacts englobing the slag of fusion of thealuminium scraps. The principal drawback of these furnaces is theproduction of a notable quantity of refusals, essentially constituted bythe salty products mixed to the slag of the process of fusion of thealuminium scrap. It originates therefore problems because of thedisposal of these refusals and not always the recycling of theserefusals is possible and convenient from an economic point of view,because it engraves in notable way on the final price of the ingot ofaluminium.

SCOPE OF THE INVENTION

The principal scope of the present invention is to avoid the drawbacksof the preceding plants realizing mainly a rotating furnace for thefusion of primary and secondary aluminium that does not have to realizethe fusion of the aluminium using a salty bath. Other scope of thepresent invention is to realize a rotating furnace for the fusion of theprimary and secondary aluminium, according with the preceding purposes,in which it is the direct and continuous pouring of the fused metal in aspherical store tank without any interruption of the process of fusion,so that to improve the use of fuel, of workforce, of salty materials,and the safety conditions of the job.

Other scope of the present invention is to get a plant of fusion of thealuminium according with the preceding purposes, that directly has anautomatic and continuous system of selection and recovery of the slag offusion integrated in the same plant, without necessity of followingtreatments in different places, so that to realize advantages in termsof costs related to the disposal of slag or its recycling.

Other scope of the present invention is to get a plant of fusion of thealuminium for the production of ingots for foundry, according with thepreceding purposes, completely modular, such that the various units,putable on track, are separable to make easy both the construction andthe assemblage of them, and the maintenance and the substitution becauseof usury.

Other scope of the present invention is to get a plant of fusion of thealuminium for the production of ingots for foundry, according with thepreceding purposes, having a system of scavenging that allows a smallerwaste of thermal energy in the furnace of fusion and simultaneously acleaning in the gases from the heavy pollutants before the stack andquality of the air breathed by the employees in the plant decidedlyimproved in comparison to the preceding plants.

DESCRIPTION OF THE DRAWINGS AND WAY OF REALIZING THE INVENTION

Further characteristics and advantages of the invention will result moreclear from the following description and from the attached drawings,furnished to only indicative purpose and not limitative.

The FIG. 1 shows, in a three-dimensional way, the general view of thesystem of fusion according to the present invention.

The FIG. 2 shows, in perspective section, the general view of the systemof fusion according to the present invention.

The FIG. 3 shows a longitudinal section of the general view of thesystem of fusion according to the present invention.

The FIG. 4 shows, schematically and in a lateral point of view, aportion of the spiral element with the channels realized on it.

The FIG. 5 shows, in a lateral longitudinal view, the equipment oftreatment of the slag with the disposition for the scavenging and thetracks of moving.

The FIG. 6 shows, schematically and in a general view, some component ofthe plant, mainly the store tank of the fused metal and the system ofscavenging.

Accordingly to the drawings, the furnace that realizes the fusion of theprimary and secondary aluminium (scraps), is constituted by acylindrical hollow body (1), with circular section, built in refractorymaterial, resistant to the thermal stress; on an extremity the body (1)is closed by a porthole (2) used for the loading of the metallic scraps;on the other extremity it is the window of entry (3) of the flame ofheat of the scrap and downward the hole (4) for the leakage of the fusedliquid that, as illustrated by the drawings, is realized in a plainslot.

The inside diameter of the body (1) changes constantly along itslongitudinal axle to originate a negative inclination on the horizontalline beginning from the extremity where is the loading porthole (2) upto the extremity where is positioned the hole (4) of leakage of themelted metal. The difference of inclination among the two extremities incomparison to the horizontal line is 2 centimetres for linear meter ofthe length of the furnace.

The furnace is covered by a metallic structure and is kept in horizontalposition by metallic traverse frames (5) that place and creep on theslides (6) held on the metallic supports (7). On both the left and rightextremities of the body (1) are the openings (8) and (9) for thescavenging of the fumes that join in a single channel of evacuation(10). On the surface of the inside wall of the body (1) and along allits length, it is a spiral element (11), whose spires, in a firstfavourite and illustrated shape, are cylindrical, with circular section,with constant diameter and built in refractory material resistant to theheat and to the mechanical stress due to the action of the scrap infusion. On the spires of the spiral element (11) and in the bottom sideclose to the wall of the cylinder body (1) are a multiplicity ofgalleries or channels (12) with a favourite semicircular section.

A channel of pouring (13), realized with a suitable inclination andadequately contained in an box (14) insulated and equipped with a window(15), is placed among the hole (4) and the spherical storage basin (16)positioned on a lower plan in a pit. The basin (16) has adequately beendescribed and claimed in the patent WO 02/39044 by the same applicant.The rotating joint (17), in comparison to that described in theaforesaid patent, has a different shape, so that to realize a continuityof inclination with the channel of pouring (13).

The principal characteristics of a preferred example of realization ofthe rotating furnace, for the fusion of the primary and secondaryaluminium, are the followings:

external diameter: 500 centimetres

inside diameter: 320 centimetres

thickness of the refractory cement: 90 centimetres

length of the cylinder: 1200 centimetres

inclination for the pouring: 24 centimetres

working temperature: 750-800° C.

feeding: methane, oil

heat consumption: 750 Kcal/h for Kg/liquid aluminium produced

The furnace is maintained in a slow rotation, from one to fourrevolution/minute, on its mean axle by a gear motor.

DESCRIPTION OF THE PROCESS OF FUSION

If the melting of secondary aluminium is preferred, at first is realizedthe selection and mixing of different types of aluminium scraps, whosechemical composition has to be as close as possible to that of thedesired alloy. Then the aluminium scraps are set, through the loadingporthole (2), in the rotating furnace without addition of sodiumchloride as cover agent to prevent the oxidation of the metal.

Because of the rotation of the furnace and the special insideconformation, is obtained the mechanical remixing of the scrap in fusionwith, simultaneously, an action of carried of the material by the wallsof the furnace. The metal gradually melts and the liquid aluminium beginto rotate in the same sense of rotation of the furnace; it will alwaysbe positioned in the low part of the furnace, because the force ofgravity is higger then the carry force due to the rotation. Moreover,because of the rotational movement, joined to the inside inclination ofthe furnace, the liquid metal continually slide to the drawing hole (4)that is put in the lowest point, flowing through the small channels (12)transversally set to the spires of the body (11).

The liquid metal is protected against the oxidation of the air becauseof its low position, it is not directly licked up by the stream of thewarm gases (whose flow is horizontal and situated in the tall part ofthe furnace), and because it continually flow in the basin (16) wherethe fused metal is stored, through the pouring channel (13). The slagsremains in the tall part and are held by the spiral body (11) and, onceall the aluminium is melted and has been stored in spherical basin, aredischarged close to the loading porthole through a channel equipped witha cochlea, finishing the process of melting.

The slags, put in the channel and pushed by the cochlea, reaches themodule of selection wherein they enter from the extremity (18). Themodule of selection is constituted by three hollow metallic and coaxialcylinders, one inserted in the other, and open to the left end, and iskept in horizontal position by booms (19) and metallic traverse frames(20) that place and creep on the slides (21) joined on metallic supports(22) with the interposition of a gear carriage (23).

The cylinders (24) and (25) have the surface side equipped with holes,greater on the first cylinder (24) and smaller on the second (25) sothat it is possible the pouring of slags of different dimensions. Thewhole, constituted by the three cylinders, has put in slow rotationaround the longitudinal axle, so have a remixing of the slags as soon asthey advance along the cylinders pushed by the cochlea. The slag,according with their weight and dimensions, passes from the firstcylinder (24) up to the last one (26). Actually, in the first cylinder(24), with smaller diameter, are the slags essentially constituted byiron parts, steel, copper, that is material that has few or not putthrough the process of fusion; in the second cylinder (25) are the slagsof aluminium oxide, while in the third cylinder (26) are essentially thedusts. It is very interesting the fact that the slags, flowing, areselected as well as they are cooled. The slags, so treated, flow out ofthe extremities of the cylinders and fall in the channels (27), (28),(29) positioned everyone below a cylinder and, by a cochlea systempresent in every channel, are pushed, at almost ambient temperature, inthe storage buckets.

The recovered aluminium oxide is recycled and joined to the feedingcharge of fusion. All the exhaust gases produced in the module ofselection and recovery of the slag are carried, through canalizations,to the cap (30), and don't escape in the external environment.

It is very important that the module of selection and recovery of theslag is constituted by units, placeables on tracks, (31), so that theycan be open for inspections and maintenance.

Even if it is not represented in the drawings, the furnace of fusion isalso modular, put on carriages that are moved on tracks, to makepossible the opening.

Other great innovation is the system of scavenging, constituted by twoseparate canalizations. The warm gases, originated by the furnace offusion at a maximum temperature of 300° C., are carried through thepipeline (32) in the underground pit (33) accessible by a porthole ofinspection (34). The gases exclusively escape from the furnace offusion, because of the concomitant action due to the kinetic energy(that originates from their heat), to the expansion that they have byreaching the pit (33), to the loss of pressure produced by the chimney(35) and to the drag force produced by the air flow, at a great speed,that escapes from the extremity (36) of the pipeline (37). In the pit(33) the warm gases, because of the expansion, decrease in temperatureand also realize a first falling of the heaviest particles of pollutantagents in the gases.

All the other gases that escape from the modules, having a lowertemperature, are carried to the pipeline (37) by extractors, continuingin an underground pipeline (38) up to the chimney (35) equipped withvarious devices of cleaning of the dangerous gases for the environmentaccording to the laws in force.

Both pipelines (32) and (37) are equipped with a control valve (39) forthe automatic passage of the gases. The present system, besides theaforesaid advantages, realizes also an energetic conservation in thefurnace of fusion, because the gases are evacuated in natural way andonly in the quantity necessary to the process of combustion, not havingadditional quantities of heat for an excess of evacuation of the gases.

As previously described and illustrated, it is clear that the inventionreaches the scope. Dimensions and shapes can be adjusted according tothe demands.

1. Plant for the melting of primary and secondary aluminium, withscreening and recovery of the slags, characterized in that it uses: arotating furnace, internally equipped with a spiral element (11), thatrealizes the fusion of the aluminium not using a salty bath; a channelof pouring (13), realized with a suitable inclination and adequatelycontained in an insulated box (14) and equipped with a window (15) thatis placed among the hole (4) of the rotating furnace and the sphericalstorage basin (16) positioned on a lower plan, in a pit, and equippedwith a rotating joint (17) that realizes a continuity of inclinationwith the channel of pouring (13) so that to obtain the direct andcontinuous pouring of the fused metal in the tank; an automatic andcontinuous apparatus of selection and recovery of the slag of fusiondirectly integrated in the same plant; a double canalization of theexhaust gases.
 2. Plant for the melting of primary and secondaryaluminium, with screening and recovery of the slags, as claimed in claim1, characterized in that the furnace for the fusion of primary andsecondary aluminium (scraps), is constituted by a hollow cylindricalbody (1), with circular section, whose inside diameter constantly variesalong its longitudinal axle to originate a negative inclination on thehorizontal line, beginning from the extremity where it is the loadingporthole (2) up to the extremity where is positioned the hole (4), withplain slot, for the leakage of the fused metal.
 3. Plant for the meltingof primary and secondary aluminium, with screening and recovery of theslags, as claimed in claim 1, characterized in that the favouritenegative inclination on the horizontal line of the furnace is twocentimetres for linear meter of the length of the furnace.
 4. Plant forthe melting of primary and secondary aluminium and with screening andrecovery of the slags, as claimed in claim 1, characterized in that thefurnace is kept in horizontal position by metallic traverse frames (5)that place and creep on the slides (6) held on metallic supports (7); onboth the left and right extremities of the body (1) are the openings (8)and (9) for the escaping of the exhaust gases that flow in a singlechannel of evacuation (10).
 5. Plant for the melting of primary andsecondary aluminium, with screening and recovery of the slags, asclaimed in claim 1, characterized in that on the surface of the insidewall of the body (1) and along all its length, it is a spiral element(11), whose spires, cylindrical with circular section, with constantdiameter and built in refractory material resistant against the heat andthe mechanical stress due to the action of the scrap in fusion, have. inthe low part of the cylinder (1), close to the wall, a multiplicity ofgalleries or channels (12) with a favourite semicircular section. 6.Plant for the melting of primary and secondary aluminium and withscreening and recovery of the slag, as claimed in claim 1, characterizedin that the spires of the element (11) have an elliptical or polygonalsection.
 7. Plant for the melting of primary and secondary aluminium,with screening and recovery of the slags, as claimed in claim 1,characterized in that the galleries or channels (12) have whateversection, e.g. circular, elliptical or polygonal.
 8. Plant for themelting of primary and secondary aluminium, with screening and recoveryof the slags, as claimed in claim 1, characterized in that the rotatingmodule of selection is constituted by three metallic hollow and coaxialcylinders, one inserted in the other, and open to the left end; thecylinders (24) and (25) have the surface side equipped with holes,greater on the first cylinder (24) and smaller on the second (25), sothat in the first cylinder (24), with smaller diameter, the slag isconstituted by material that has few or not put through the process offusion, in the second cylinder (25) it is the slag constituted byaluminium oxide, while in the third cylinder (26) they are essentiallythe dusts.
 9. Plant for the melting of primary and secondary aluminium,with screening and recovery of the slags, as claimed in claim 1,characterized in that the selected slag flows out of the extremities ofthe cylinders pushed by cochlea and falls in the channels (27), (28),(29) positioned everyone below a cylinder and, by a cochlea systempresent in every channel, are pushed, at almost ambient temperature, inthe store buckets.
 10. Plant for the melting of primary and secondaryaluminium with screening and recovery of the slags, as claimed in claim1, characterized in that the module of selection and recovery of theslag is constituted by units, placeables on tracks (31), so that it canbe open for inspections and maintenance.
 11. Plant for the melting ofprimary and secondary aluminium with screening and recovery of the slag,as claimed in claim 1, characterized in that the process of meltingconsists in the following phases: a) in case of favourite melting ofsecondary aluminium, is realized the selection and mixing of differenttypes of aluminium scraps, whose chemical composition has to be as closeas possible to that of the desired alloy; b) the aluminium scraps areplaced, through the loading porthole (2), in melting in the rotatingfurnace without addition of sodium chloride as cover agent to preventthe oxidation of the metal; c) because of the rotation of the furnaceand the special inside conformation, is obtained an action of mechanicalremixing of the scrap in fusion, joined to an action of dragging by thewalls of the same furnace; d) the metal gradually melts and the liquidaluminium begins to rotate in the same sense of rotation of the furnace;it will always be positioned in the low part of the furnace, because theforce of gravity is higher then the drag force due to the rotation; e)the rotational movement, in association with the inside inclination ofthe furnace, will provides that the liquid metal continually flow towardthe drawing hole (4) that is set in the lowest point, passing throughthe small channels (12) transversals to the spires of the body (11); f)the liquid metal is protected against the oxidation, because it is verylower then the stream of the warm gases and because it continually flowin the storage basin (16) through the channel of pouring (13); g) theslag remains in the tall part, and is held by the spiral body (11) anddischarged close to the loading porthole; from there it reaches achannel equipped with a cochlea, that pushes them until the extremity(18) of the module of selection; h) the slag are shared, according todimension and weight, in inert and ferrous material (having an highpoint of fusion), in aluminium oxides and dusts and introduced,automatically, in the respective channels, equipped with a cochlea; fromthere it flows into the store buckets; i) the recovered aluminium oxideis recycled to integrate the feeding charge of fusion.
 12. Plant for themelting of primary and secondary aluminium with screening and recoveryof the slags, as claimed in claim 1, characterized in that the warmgases that originate from the furnace of melting, at a maximumtemperature of 300° C., are carried through the pipeline (32) in theunderground pit (33).
 13. Plant for the melting of primary and secondaryaluminium, with screening and recovery of the slags, as claimed in claim1, characterized in that the gases escape exclusively from the furnaceof melting because of the concomitant effect of the kinetic energy dueto their heat, of the expansion that they have reaching the pit (33), ofthe loss of pressure produced by the chimney (35) and of the draggingproduced by the air flow, having an high speed, that escapes from theextremity (36) of the pipeline (37).
 14. Plant for the melting ofprimary and secondary aluminium with screening and recovery of theslags, as claimed in claim 1, characterized in that the exhaust gasesthat escape from the modules of selection and recovery of the slag andfrom the store basin, having a low temperature, are carried to thepipeline (37) by extractors, to continue then in an underground pipeline(38) up to the chimney (35).
 15. Plant for the melting of primary andsecondary aluminium, with screening and recovery of the slags, asclaimed in claim 1, characterized in that both the pipelines (32) and(37) are equipped with a control valve for the automatic passage of thegases.